draft-ietf-dhc-subnet-option-01.txt   draft-ietf-dhc-subnet-option-02.txt 
Network Working Group G. Waters Network Working Group G. Waters
INTERNET-DRAFT Nortel Networks INTERNET-DRAFT Nortel Networks
March 1999 June 1999
The Subnet Selection Option for DHCP The Subnet Selection Option for DHCP
<draft-ietf-dhc-subnet-option-01.txt> <draft-ietf-dhc-subnet-option-02.txt>
Tuesday, March 23, 1999, 4:35 PM
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with all This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026. provisions of Section 10 of RFC2026.
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (1999). All Rights Reserved. Copyright (C) The Internet Society (1999). All Rights Reserved.
Abstract Abstract
This memo defines a new DHCP option for selecting the subnet on which This memo defines a new DHCP option for selecting the subnet on which
to allocate an address. This option would override a DHCP server's to allocate an address. This option would override a DHCP server's
normal methods of selecting which subnet on which to allocate an normal methods of selecting the subnet on which to allocate an address
address for a client. for a client.
Waters Expires: Jun 1999 + 6 months [Page 1]
Table of Contents Table of Contents
1. Introduction......................................................2 1. Introduction......................................................2
2. Subnet Selection Option...........................................3 2. Subnet Selection Option...........................................3
3. Intellectual Property.............................................4 3. Intellectual Property.............................................4
4. Acknowledgements..................................................4 4. Acknowledgements..................................................4
5. Security Considerations...........................................4 5. Security Considerations...........................................4
6. References........................................................4 6. References........................................................5
7. Editor's Addresses................................................5 7. Editor's Addresses................................................5
8. Full Copyright Statement..........................................5 8. Full Copyright Statement..........................................5
1. Introduction 1. Introduction
This memo was produced by the DHCP Working Group and defines a new This memo was produced by the DHCP Working Group and defines a new
DHCP option that specifies the subnet on which a DHCP server should DHCP option that specifies the subnet that a DHCP server should use
use when selecting an address. This option takes precedence over when selecting an address. This option takes precedence over other
other methods that the DHCP server may use to determine the subnet on methods that the DHCP server may use to determine the subnet on which
which to select an address. Two existing methods of determining the to select an address. Two existing methods of determining the subnet
subnet on which to select an address are: on which to select an address are:
o To use the subnet address of the giaddr field in the DHCP packet, o To use the subnet address of the giaddr field in the DHCP packet,
or if the giaddr field is zero; or if the giaddr field is zero;
o To use the subnet address of the local interface on which the o To use the subnet address of the local interface on which the
packet was received by the DHCP server. packet was received by the DHCP server.
Methods other than the two described above may exist. Methods other than the two described above may exist.
The subnet selection option is useful, but not limited to, the class The subnet selection option is useful for, but not limited to, the
of devices that have a packet-handling plane (e.g.: switching, routing class of devices that have a packet-handling plane (e.g.: switching,
functionality) and a control plane (e.g.: device management and routing functionality) and a control plane (e.g.: device management
control functionality). The control plane is network connected and and control functionality). The control plane is network connected and
there is a DHCP server connected to that network. The packet-handling there is a DHCP server connected to that network. The packet-handling
plane may or may not be network connected, however, in either case plane may or may not be network connected, however, in either case
there is no network connected DHCP server available to this plane. The there is no network connected DHCP server available to this plane. The
control plane is not network connected to the packet-handling plane, control plane is not network connected to the packet-handling plane,
although the two planes may communicate using some method (e.g.: an although the two planes may communicate using some method (e.g.: an
internal data bus). internal data bus).
For the networks to which the packet-handling plane is connected, There is a requirement to allocate addresses for devices connected to
there is a requirement to allocate addresses for devices connected to the networks to which the packet-handling plane is connected.
those networks.
Since there is no network connectivity between the DHCP server and the Since there is no network connectivity between the DHCP server and the
packet-handling plane, the control plane must allocate addresses using packet-handling plane, the control plane must allocate addresses using
the DHCP on behalf of the packet-handling plane. Because the control the DHCP on behalf of the packet-handling plane. Since the control
plane is requesting the addresses, the DHCP server would normally have plane is requesting the address, the DHCP server would normally
the undesired result of allocating the address on the subnet on which
the control plane is connected. Waters Expires: Jun 1999 + 6 months [Page 2]
allocate the address on the subnet on which the control plane is
connected, which would not be the desired result.
If the option specified by this memo is included in the If the option specified by this memo is included in the
DHCPDISCOVER/DHCPREQUEST message then the server should allocate an DHCPDISCOVER/DHCPREQUEST message then the server should allocate an
address on the subnet or network segment that is specified by this address on the subnet or network segment that is specified by this
option. The option would specify an address of one of the packet- option. The option would specify an address on one of the packet-
handling plane's subnets. handling plane's subnets.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. Subnet Selection Option 2. Subnet Selection Option
The subnet selection option is a DHCP option. The option contains a The subnet selection option is a DHCP option. The option contains a
single IP address that is the address of a subnet. The value for the single IP address that is the address of a subnet. The value for the
subnet address is determined by taking any IP address on the subnet subnet address is determined by taking any IP address on the subnet
and ANDing that address with the subnet mask (i.e.: the network and and ANDing that address with the subnet mask (i.e.: the network and
subnet bits are left alone and the remaining (address) bits are set to subnet bits are left alone and the remaining (address) bits are set to
zero). When this option is present, the DHCP server MUST use either zero). When this option is present, the DHCP server MUST use either:
the:
o The subnet specified in the option, or; o The subnet specified in the option, or;
o A subnet on the same network segment as the subnet specified in the o A subnet on the same network segment as the subnet specified in the
option; option;
on which to allocate an address. on which to allocate an address.
The format of the option is: The format of the option is:
Code Len IP Address Code Len IP Address
+-----+-----+-----+-----+-----+-----+ +-----+-----+-----+-----+-----+-----+
| TBD | 4 | A1 | A2 | A3 | A4 | | TBD | 4 | A1 | A2 | A3 | A4 |
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The format of the option is: The format of the option is:
Code Len IP Address Code Len IP Address
+-----+-----+-----+-----+-----+-----+ +-----+-----+-----+-----+-----+-----+
| TBD | 4 | A1 | A2 | A3 | A4 | | TBD | 4 | A1 | A2 | A3 | A4 |
+-----+-----+-----+-----+-----+-----+ +-----+-----+-----+-----+-----+-----+
In order to ensure backwards compatibility of clients that do support In order to ensure backwards compatibility of clients that do support
this option when communicating with DHCP servers that do not support this option when communicating with DHCP servers that do not support
this option, the DHCP client SHOULD check that an allocated address in this option, the DHCP client SHOULD check that an allocated address is
on the requested subnet or network segment. The client SHOULD NOT on the requested subnet or network segment. The client SHOULD NOT
respond to a DHCPOFFER or DHCPACK of an address that is not on the respond to a DHCPOFFER or DHCPACK of an address that is not on the
requested subnet or network segment. requested subnet or network segment.
This option does not require any change to other operations or Servers supporting this option MUST return the option to any client
features of the DHCP server other than to select the subnet on which that sends it, regardless of whether or not the client requests it in
to allocate an address. For example, the handling of DHCPDISCOVER for a parameter request list. Clients using this option must discard
an unknown subnet may continue to operate unchanged. DHCPOFFER or DHCPACK packets that do not contain this option.
Waters Expires: Jun 1999 + 6 months [Page 3]
This option does not require changes to operations or features of the
DHCP server other than to select the subnet on which to allocate an
address. For example, the handling of DHCPDISCOVER for an unknown
subnet may continue to operate unchanged.
When this option is present and the server supports this option, the When this option is present and the server supports this option, the
server MUST NOT offer an address that is not on the requested subnet server MUST NOT offer an address that is not on the requested subnet
or network segment. or network segment.
Existing methods for determining where to send a reply to a DHCP The IP address to which a DHCP server sends a reply to MUST be the
client are not changed when this option is present in a request. same as it would chose when this option is not present.
3. Intellectual Property 3. Intellectual Property
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to pertain intellectual property or other rights that might be claimed to pertain
to the implementation or use of the technology described in this to the implementation or use of the technology described in this
document or the extent to which any license under such rights might or document or the extent to which any license under such rights might or
might not be available; neither does it represent that it has made any might not be available; neither does it represent that it has made any
effort to identify any such rights. Information on the IETF's effort to identify any such rights. Information on the IETF's
procedures with respect to rights in standards-track and standards- procedures with respect to rights in standards-track and standards-
skipping to change at page 4, line 34 skipping to change at line 181
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive this standard. Please address the information to the IETF Executive
Director. Director.
4. Acknowledgements 4. Acknowledgements
This document is the result of work undertaken the by DHCP working This document is the result of work undertaken the by DHCP working
group. Thanks to Tim Aston and Ralph Droms for reviewing this memo. group. Thanks to Ted Lemon, Tim Aston and Ralph Droms for their
helpful comments in this work.
5. Security Considerations 5. Security Considerations
DHCP currently provides no authentication or security mechanisms. DHCP currently provides no authentication or security mechanisms.
Potential exposures to attack are discussed is section 7 of the Potential exposures to attack are discussed is section 7 of the
protocol specification [RFC2131]. protocol specification [RFC2131].
Waters Expires: Jun 1999 + 6 months [Page 4]
6. References 6. References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP 14, March 1997. Requirement Levels", RFC 2119, BCP 14, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
March 1997. March 1997.
[RFC2132] Alexander, S. and Droms, R., "DHCP Options and BOOTP Vendor [RFC2132] Alexander, S. and Droms, R., "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997. Extensions", RFC 2132, March 1997.
skipping to change at line 225 skipping to change at line 239
The limited permissions granted above are perpetual and will not be The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns. revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT
NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN
WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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